Generally, bimetal coins or medals are metal assemblies made of different metals which are used to prevent counterfeits and to upgrade a product high quality. Such a bimetal coin or medal is configured of an external coin for defining an external appearance and an internal coin coupled to the external coin.
Such the bimetal coin (coupling body of the external and internal coins) is configured of two kinds of metals coupled to each other. because of that, even if quite a shock is applied to the bimetal coin, the bimetal coin is required not to be separated into the external coin and the internal coin which are made of different metals.
According to a conventional bimetal coin, a recess is formed in an inner surface of an external coin and a predetermined projection is formed in an outer surface of an internal coin to be inserted in the recess of the external coin. When the internal coin is insertedly coupled to the external coin, the internal coin is stretched for the projection formed in the outer surface of the internal coin to be inserted inn the recess formed in the inner surface of the external coin. As a result, the internal coin and the external coin are coupled to each other.
In the meanwhile, according to another type of the conventional bimetal coin, a projection is formed in the inner surface of the external coin and the internal coin is formed in a simple circular shape. It is well-known that the internal coin is stretched enough to surround the projection of the external coin, as it is intertedly coupled to the external coin.
However, according to the above two types of conventional bimetal coins, it is required to form the recess or projection in the inner surface of the external coin.
Because of that, it is very difficult and it costs quite a lot to form the inner surface of the external coin. Without exclusive equipment for forming the inner surface, it is impossible to process the inner surface of the external coin.
Moreover, in case of a bimetal coin or medal having a small inner diameter of an external coin, it is commercially impossible to process a recess or projection in the small inner surface.
Alternatively, different from the above conventional ones, a recess portion is formed in a center of an outer surface of an inner coin along a circumference direction and an external coin is thicker than the inner coin, without any process of an inner surface of the external coin. When the inner coin is insertedly coupled to the external coin after that, an inner portion of the external coin is plastically inserted in the recess portion of the inner coin, to couple the external and inner coins to each other. This technology is included in the conventional art to which the present invention pertains.
However, that technology goes against natural metal flow generated in the pressingly inserted process.
In other words, the natural metal flow (the direction of the metal stretching generated in the plastic transformation) generated in the inserted coupling process will occur toward a direction of increased inner and outer diameters. In contrast, according to above technology, the recess portion is formed in the center of the outer surface of the inner coin. Because of that, during the insertedly coupling process, the size of the recess portion happens to be decreased by the metal flow.
As a result, when fabricating the bimetal coin or medal by using the above technology, the outer diameter of the external coin is molded during the insertedly coupling process. Because of that, extra metal which is the external coin (the metal amount transformed by the pressing of the insertedly coupling process) has to be forced to flow into the recess portion of the internal coin, with plastically transformed. Thus, there would be a problem of an external press requiring a large energy which has to be applied. The coupling between the external and internal coins cannot help deteriorating, because it goes against natural metal flow.
Furthermore, all of the above conventional inventions disclose only the structure configured of two elements including the inner coin (insert) and the external coin (external ring), failing to disclose a new type of coins or medal applicable to fabricate a more highly cost coin or commemoration medal.